It is of significant importance to extract biologically active substances, for example, cells, proteins and nucleic acids in various areas such as modern clinical disease diagnosis, blood transfusion safety, forensic identification, surveillance of microorganism in environmental applications, food safety detection and molecular biology. Among these, nucleic acid, as a biologically active substance compound built by a plurality of nucleotides polymerized together, is one of the most essential substances for life. Nucleic acid can be widely found inside animal cells, plant cells, microorganisms and organisms. On the basis of different chemical compositions, nucleic acids may be categorized as ribonucleic acid (which is referred to as RNA for short) and deoxyribonucleic acid (which is referred to as DNA for short). DNA is the primary material base for storing, reproducing and transferring hereditary information, while RNA plays an important role in the process of protein synthesis. As biological technologies develop rapidly and the polymerase chain reaction (PCR) technique is widely applied in various areas, including disease diagnosis in medical industry, genetic modification detection in agriculture and many other areas, a method and an instrument for high-throughput extraction of biologically active substances from samples and for automatic extraction of biologically active substances are highly demanded.
It is a new technology that has been developed in recent years to extract biologically active substances, particularly, active macromolecules, through a magnetic particle method. The magnetic particle method refers to utilization of magnetic particles which are capable of recognizing specificity of cells, proteins or nucleic acids, and the magnetic particles can specifically combine with nucleic acid molecules, and thence separate active macromolecules from samples of blood, animal tissues, food, pathogenic microorganisms and the like under the effect of a magnetic field. For example, according to a principle same as the principle for silica spin column, extraction of a nucleic acid through magnetic particle method can fabricate superparamagnetic silicon oxide Nano-magnetic particles through making modification to the surface of superparamagnetic Nano-particles by means of Nano technology. The magnetic particles of this kind are capable of recognizing specificity of nucleic acid molecules. By means of the superparamagnetic nature of silicon dioxide Nano particles, DNA and RNA can be extracted from a sample in the presence of a chaotropic salt (e.g., guanidine hydrochloride, guanidinum thiocyanate, etc.) under the effect of an external magnetic field.
Automatic extraction instruments applying a magnetic particle method can be categorized into ones applying magnetic rod technique and ones applying suction process. The suction process is conducted by means of an automatic liquid transfer device. Take the nucleic acid extraction instrument through a magnetic particle method as an example, an automatic liquid transfer device may be used to add lysis buffer, and to attract magnetic particles; to suction a solution away, to add a rinsing liquid, to attract magnetic particles, to suction the rinsing liquid away, and to add an elution buffer solution. However, because the suction process is subject to a problem of retaining magnetic particles at the meantime of removing waste liquids, the liquid transfer device cannot be placed too close to magnetic particles; and this in turn affects the elution efficiency and purification.
Extraction through magnetic rod technique is a technology that has been developed in recent years and the working principle behind it is to immerse a magnetic separation device into a liquid so as to enable particles, which are capable of being magnetically attracted, in the mixture to aggregate on the surface of the separation device under the effect of a magnetic field. In one of the modes, the magnetic separation device is a sleeve, and insertion of a magnetic rod makes the sleeve magnetic and enables particles, which are capable of being magnetically attracted, in the mixture to aggregate on the surface of the sleeve; the sleeve is no longer magnetic when the magnetic rod is taken out from the sleeve, and thus the particles magnetically attracted then are separated from the surface of the sleeve. The through-put of a nucleic acid extraction instrument through magnetic rod technique is usually equipped with 8, 16, 32 or 96 channels; as compared with a suction process, the advantage of the magnetic rod technique is that there is no liquid residue at each step since the magnetic rod only takes magnetic particles and transfers the same into corresponding reaction wells at subsequent steps. The mechanism for moving the magnetic rod in an instrument applying the magnetic rod technique is capable of moving the rod upward and downward in the sleeve, which is favorable for operations of lysis, resining and purification in the extraction process.